Scientists and crew inspecting the net of our first bottom trawl
A Spectrunculus grandis, one of the largest species captured
Date:July 8, 2004
Author: Franz Uiblein (IMR, Norway), Marsh Youngbluth (Harbour Branch Oceanographic Institution, USA)
We are currently working stations on the western flank of the mid-Atlantic Ridge north of the Azores (Southern MAR-ECO box). The depth is between 1500 and 3000 m. After detailed bathymetric seabed mapping with the sophisticated SIMRAD EM 300 multibeam echosounder and a CTD station, the trawl equipped with an additional plankton net on top and a video camera in the opening has been launched. The mapping has allowed selection of an appropriate bottom type with mainly soft sediments where the trawl can be operated efficiently. In the trawl yesterday (approx. 3000m) and in todays trawl at around 2000m, the catch exceeded all our expectations: a great number and diversity of fishes including rattails, halosaurids, smoothheads, and lizardfishes including one big individual of the species Bathysaurus mollis. Among the invertebrates a great number of large holothurians (sea cucumbers) dominated the catch accompanied by an array of bottom fauna. Also cephalopods and shrimps that live in the open water above the bottom were caught. Fish biologists and taxonomists as well as our benthos specialist were very busy till late night sorting and identifying the species, taking sub-samples and transferring the data into the MAR-ECO database.
In concert with the results from the collections in the open water during the first leg of this cruise, the species composition and distribution of the fauna sampled with the bottom trawl along the ridge will provide us interesting insights into the role of the ridge itself as providing a suitable habitat for a diversity of mobile and sedentary fauna. For fishes encountered at deep-sea bottoms often the expression “demersal” is used indicating a bottom-associated lifestyle that may be accompanied by extensive excursions into the open water in some of them. Therefore fishes provide a good group to study so-called “benthopelagic interactions” between the life at the bottom and in the open water. Such interactions can be also studied by direct “in situ” observations as planned with the two ROVs (remotely operated vehicles) on board or by investigating the stomach samples that have been taken from the dominant fish species for further analysis of foraging behaviour and food-web relationships. Also the trawl camera will provide valuable information on the behaviour of fishes that are later collected by this gear.
Among the fishes also a species of the Family Ophidiidae was found belonging to the genus Spectrunculus that was also numerous in the catch of the longliner MS Loran that operated in parallel in the eastern part of the ridge and reported steady catches. If this fish would be given a common name, it might be called “giant brotula”, as it reaches a size of more than 120 cm. The species identity shall be clarified during further taxonomic work at the Bergen Museum where all the collected material will be stored after this cruise. Till then however we expect a lot more exciting material and information.